The present invention relates to the general technical field of printing on a flat substrate, for example a fabric, by reference to which the present invention will be introduced, discussed and exemplified.
By xe2x80x9cfabricxe2x80x9d is meant generically any woven or nonwoven cloth.
The invention is concerned more particularly with printing on a fabric of the xe2x80x9cjacquardxe2x80x9d type. Such printing must make it possible to print an image, a design or colors on a figured pattern pre-existing in the fabric.
In all the description and the claims below, the term xe2x80x9cpatternxe2x80x9d in the singular designates a unitary or single pattern or one which is repeated in at least one direction or dimension of the flat substrate, for example of the fabric, and a set of patterns identical or different from one another.
Patterns of the xe2x80x9cjacquardxe2x80x9d type are produced by different ways of interlacing the threads, thus giving said patterns their form, their contour and a surface or textured appearance, with some contrast. The patterns are therefore figured directly in the fabric.
Traditional printing, known as xe2x80x9cflat-screenxe2x80x9d printing, is defined as being printing in which a printing screen is used. The latter has a cutout according to the form of a pattern.
A mask is a band of greater or lesser length which is arranged on the fabric and is provided with cut-out patterns.
Printing known as xe2x80x9cdouble-stencilxe2x80x9d printing is defined as being printing in which a printing screen is superposed on a mask, in order to carry out screen printing.
Printing methods are known which involve accurately fastening a fabric to a table and manufacturing very expensive printing screens which are arranged successively on the fabric, so as to produce prints through said screens in a way in register with the figured patterns of the fabric. Such a method requires considerable human resources in order to position the fabric and/or the printing screens. The fastening of the fabric to a table is a very time-consuming manual operation.
Such a method assumes the use of fixed-form screens which do not make it possible to obtain high accuracy. An accuracy of the order of a centimeter is obtained, which may represent an appreciable offset during printing.
It is also known, from the document DE 3 917 957, to employ a method for printing a fabric with designs and/or colors, which involves:
pre-recording a pattern with the aid of a camera or computer;
where appropriate, processing the pre-recorded pattern;
and generating a printing file comprising data relating to the pre-recorded and/or processed pattern, so as to control the printing from a printer connected to the computer. The fabric is thus printed with the patterns pre-recorded in the computer, for example repetitively.
This method does not make it possible to identify and recognize a pre-existing pattern in the fabric.
Moreover, such a method, by its very conception, is independent of the structure of the fabric and, more specifically, of any distortion of the pattern figured in the fabric. There is no provision for adapting to the pattern figured in the fabric.
The document EP 0 795 400 relates to a printing method for printing a substrate, in this particular case paper. This method involves pre-recording at least one pattern numerically, generating a printing file comprising data relating to the pre-recorded pattern and carrying out printing generated directly or indirectly from the printing file.
Reference patterns are recognized, using a shade separation technique. This technique is implemented by successively generating elementary images corresponding to shades or to superpositions of particular shades. The elementary images, obtained by means of screens, cylinders or printing presses, are positioned in relation to one another in order to come as closely as possible to the pre-recorded reference patterns.
The various shades, applied in successive layers, are therefore repositioned in relation to one another in order to obtain the final image. Moreover, repositioning is controlled by means of a comparison between a reference image and the actual printed image resulting from a printing test.
For processing purposes, this method allows only a relative displacement between fixed or unchangeable images.
The method is implemented in a printing technique, not by the continuous printing of a fabric, on which it is necessary to identify, analyze and process a pattern integrated into the substrate, said pattern not necessarily being repeated identically in its form and/or its position on the substrate.
This method does not make it possible to modify the geometry of a pattern substantially in the measurement or the paper printing press used does not make it possible to set the relative positioning of elementary shades.
The essential object of the present invention is a method making it possible to print any pattern on a flat substrate, for example a fabric, in a recorded or identified manner with respect to any pre-existing pattern on said fabric, and, in particular, any figured pattern.
According to the invention, the printing method involves:
continuously or discontinuously identifying at least one pattern of a fabric by relative displacement between said fabric and an image acquisition means;
comparing the identified pattern in real time with a reference pattern pre-recorded for recognition purposes;
adapting the pre-recorded reference pattern in line, in order to superpose it on and/or fit it to the identified pattern, and generating a printing file;
and carrying out printing dot by dot, directly or indirectly, according to the printing file.
The objects assigned to the present invention are also achieved with the aid of a xe2x80x9ccomputer programxe2x80x9d product loadable directly into the internal memory of a computer and comprising software code portions for executing the steps of the method described below, when said program is executed on a computer.
The present invention also relates to an assembly for printing on a substrate, comprising:
a camera for recording a reference pattern;
a computer connected to said camera, in order to store and, where appropriate, modify data relating to the reference pattern;
and a printer, of which at least one head for printing dot by dot is controlled by a printing file generated by the computer.
According to invention, the printing assembly comprises:
a means for the support and movement of the substrate;
analysis means in order, on the one hand, to compare a pre-recorded reference pattern in real time with a pattern identified on the substrate, and, on the other hand, to adapt or not the data relating to the reference pattern as a function of the result of the comparison;
and means for generating a printing file from the data modified or not.
The method according to the present invention has the advantage of making it possible to print fabrics for which it is not possible to recognize by transparency patterns which are figured in said fabric.
Another advantage is linked to the automation of the printing operations and, in particular, the identification of the patterns figured in the fabric.
This automation also relates to the printing operation per se which may be carried out directly from pre-recorded instructions. The printing method according to the invention makes it possible to carry out detailed work automatically, in line, on the form of the images to be printed, in order to obtain an accurate register with respect to the form and position of the pre-existing pattern of the fabric.
Such a pattern may be defined, in particular, in relation to the edges of the fabric.
Another advantage of the method according to the invention is the possibility of combining some steps with traditional printing, for example using printing screens. In fact, such a combination makes it possible to obtain special interesting esthetic effects.
Continuous adaptation to the patterns figured in the fabric makes it possible to take into account, on the one hand, the actual positionings of said patterns and, on the other hand, possible deformations or distortions of said patterns attributable, for example, to manufacturing defects or to mounting faults on the means for the movement of the fabric. The fabric may, for example, be locally tensioned to a greater or lesser extent in relation to the movement members, thus generating an offset or a deformation of one or more patterns.
Another unexpected advantage of the method according to the invention is that it is free of the limitations imposed by a pre-recorded and unchangeable reference model or pattern.
In fact, this reference pattern may, according to the invention, be processed or adapted in such a way as to be identified as closely as possible with the actual pattern read and recognized on the fabric. In contrast to screen printing and cylinder printing, the image to be printed is thus constructed completely or partially as the fabric moves past in front of the camera. During this construction, the pre-recorded pattern is used, which is converted by displacement and/or deformation so as to be superposed on the actual pattern figured in the fabric.
According to the invention, preferably, the fabric is moved in relation to an identification means and to a printing means at a speed compatible with the identification speed and the printing speed.
According to the invention, preferably, printing is adapted in line by means of the virtually instantaneous recognition of different pre-existing patterns capable of succeeding one another or alternating with one another on the fabric.
The method according to the invention makes it possible to print patterns in situations where traditional screen or cylinder printing does not afford sufficient accuracy with respect to a pre-existing pattern on the fabric.
As an example, even if the fabric is tensioned so as to deform the patterns which are figured on it (jacquard fabric), these deformed patterns are recognized and accurately overprinted. When the fabric is subsequently relaxed, the figured patterns resume their initial form which will remain correctly printed. There will be no offset between the figured patterns and the printed patterns corresponding to all the reference patterns.